The Art and Science of D&D Encounter Building
The question recently came up at Nerdarchy whether the fifth edition D&D encounter building system is art or science with regard to the experience point guidelines set out in the Creating Encounters section of the Dungeon Master’s Guide. I am in the camp that says it is both art and science.
Building D&D encounters as a science
The science of encounter building is what is laid out in the Creating Encounters section of the DMG, and veteran Dungeon Masters will recognize the guidelines presented arise from considerations about the action economy between the player characters and the monsters. If the efficacy of the player characters’ actions and those of the monsters is approximately the same, then it stands to reason the side that gets the most actions per turn is going to have the advantage.
If the average player character action outshines that of the average monster action, then the encounter will only be challenging if the monsters outnumber the player characters. If it’s the other way around, such as in the classic scenario where an adventuring party goes up against a Big Bad that has a few powerhouse actions, then the extra actions the players get relative to the monster are what even the field.
This is the fundamental mechanic that underlies all of the considerations discussed in the Creating Encounters section of the DMG, and it forms the technical basis on which to apply the art of encounter design.
As monsters scale up in difficulty, not only do they tend to accrue more actions per round that they can use, but the actions themselves tend to be more effective. This is true of the player characters as well, and all of this is built into the logic of the XP Thresholds By Character Level chart on page 82 of the DMG. It is also the logic behind the tier system described in the Tiers of Play section in the Player’s Handbook; just looking at the fighter as a guideline, we see it gets its second attack in the second tier, its third attack in the third tier, and its forth attack in the forth tier. These do not represent more actions, but they do represent a gain in action efficacy.
The same can be seen in the damage progression for cantrips for spellcasters. While it is not as explicit or obvious in the case of monsters, they also generally follow a similar progression, and monsters are generally designed to serve as opponents for player characters of a given tier. This notion is the origin of the advice on page 82 of the DMG:
“When making this calculation, don’t count any monsters whose challenge rating is significantly below the average challenge rating of the other monsters in the group, unless you think the weak monsters significantly contribute to the difficulty of the encounter.”
What this is essentially saying is monsters that would not even rate as a deadly encounter for a single character two or more tiers below that of the party probably shouldn’t even count toward the XP threshold for an encounter. It’s not that they don’t add extra actions to the side of the monsters, but their actions are so ineffective compared to those of the player characters, they tend to barely make a difference.
With all of that said, one of the earliest guidelines we are introduced to in fifth edition D&D is on page 7 of the PHB, in the Specific Beats General section. This is true not only of the exception-based game mechanics driving D&D play, but also in aspects of the design itself. We can think of the above encounter science as the general rule, but the art is how those general rules all play out in specific circumstances with a specific party composition.
Building D&D encounters as an art
The easiest way to grasp how specificity overrides the general in the art of D&D encounter building is with an example. Consider a party of melee bruisers with great physical attributes and saves, but very poor mental attributes and saves. If this group comes up against a stone giant and the table on page 82 of the DMG suggests the encounter is of medium difficulty, then there is a good chance the player characters will prevail.
The tough player characters will be able to withstand the giant’s barrage of attacks long enough that all of their own damage output can overcome it.But what if that same group is up against a mind flayer? A stone giant and a mind flayer are worth the same XP, but how are a bunch of oafish bruisers going to hold up to a Mind Blast or two? A rookie DM might run both scenarios over the course of a campaign and conclude that stone giants are weak or that mind flayers are overpowered, and while the argument can certainly be made that mind flayers punch above their weight, a major factor in how encounters turn out is party composition. And in the case of mind flayers, what makes it seem like they should be worth more XP is that a lot of players use Intelligence as a dump stat. That says nothing objective about these two monsters, but it does show how context is critical for determining encounter difficulty.
Context can be important even when talking about the same monster. Consider, for instance, the case of a third-tier party going up against an adult green dragon. Going by the XP Thresholds By Character Level chart, this creature would rate as a hard encounter for a group of five 12th-level characters. But, characters of this level have a lot of countermeasures at their disposal for countering green dragons.
For example, several different spellcaster classes have access to the protection from poison spell, which grants resistance to poison damage and advantage on poison saving throws, which greatly reduces the damage output of the dragon’s breath weapon. Many characters may also have access to heroes’ feast, which grants immunity to both the breath weapon and Frightful Presence ability of the dragon. The context that may well matter most of all, then, is whether the party knows they are going to face a green dragon, or whether it happens completely out of the blue.
A party that is plotting a raid on a green dragon’s lair can take time to prepare, whereas a party caught off guard by a green dragon will have none of these spells in place, and may not even have them at their disposal to use at all. In both cases, we’re talking about the same monster and the same party of characters, but the outcome could hinge entirely on the context of the encounter and have little to do with the XP value given for an adult green dragon.
Environment can also play a major role in how difficult an encounter is. Given the typical character with darkvision has it out to a range of 60 ft. (with exceptions here and there), and most light sources produce light to about the same range, the prospect of fighting a drow or horned devil or beholder, all of which can see in the dark out to 120 ft., becomes a lot more menacing when going from a dark 30 x 30 room to a dark 300 x 300 cavern chamber.
The latter scenario means the bad guy might get the drop on the party before they even notice it, not to mention it can maneuver around in the dark to keep them guessing as to its location. This could represent the party spending valuable actions just trying to find the enemy in a bigger space, when they could have already closed and be attacking it in a more confined space. If encounters in your game routinely seem too difficult or too easy, you might consider adjusting the environment. In my experience, monsters are meant to be encountered in terrain and spaces that play to their strengths; a red dragon in a volcano makes a lot more sense and is a lot more deadly than a red dragon living on the seafloor.
As suggested by the first example of a party of melee bruisers up against a stone giant or a mind flayer, context includes both the monsters and the player characters. To turn to the beholder again for a case study, we can figure one of the most effective ways to shut one down is to blind it. This may be difficult to pull off on account of its good saving throws and Antimagic Cone, but it is far from impossible. As described in the Eye Ray action, a beholder must see something to target it. If you can blind it, not only do you shut down its best action, but you shut down all three of its legendary actions. You go from having your party trying to withstand six eye rays per round to zero; the beholder’s offensive capabilities go from extremely potent to a mediocre bite attack that it can attempt to make with disadvantage on account of being blinded.
The art of crafting and building D&D encounters, then, is in the DM knowing the capabilities of the party. Can the party blind or stun or otherwise attempt to shut down the beholder’s eye rays? Will the environment in which they encounter the beholder permit them to do that, or will they be severely hindered in trying to engage it? Depending on the answers to these questions, a beholder encounter could go from being a potential total party kill to a cakewalk, even if the numbers on the XP chart suggest it is a medium encounter.
This interplay between character and monster capabilities also plays out in whether monster or player capabilities are relevant. For instance, if a party makes use of almost no spells that require saving throws, then the Magic Resistance trait will be of virtually no value to the monsters. In such an encounter, the monsters may seem to be wildly underpowered for the XP total they represent.
On the other hand, if the party has a bunch of offensive spellcasters that use spells with saving throws, then the trait may come up every round and make a substantial difference to the outcome. Looking at things from the other side, if the party has a plethora of traits, spells, and magic items that grant them resistance to fire, what good is that against a blue dragon? In such a scenario, a red dragon — which is worth more XP — may prove to be a lesser challenge than a blue dragon, which is ostensibly slightly weaker. Endless examples abound: how tough is an invisible stalker if the whole party can see invisible? How useful is a see invisibility spell to one of the party’s spellcasters if none of the foes can become invisible? Once again, it comes down to the DM knowing what capabilities each side has in an encounter, and knowing what those capabilities are really worth. That is the art of D&D encounter building.
D&D encounter building is art and science
As with so many things in life, Dungeon Mastering is both art and science, so it should come as no surprise that individual elements of Dungeon Mastering, such as encounter building, comprise both art and science. Science represents the knowledge of how things work, whereas art lies in applying that knowledge.
In the context of games, the science manifests as familiarity with the rules, both in an encyclopedic sense and in a logical sense (why they are the way they are), whereas the art is understanding why the other players are there, and in the case of a cooperative game like D&D, applying knowledge of the mechanics to help everyone at the table accomplish their goals, both shared and individual.
In some D&D games, this could mean a series of fine-tuned encounters that push the party to the brink. In other games, it could mean encounters where combat can be circumvented altogether, but when combat does break out, the characters can expect to steamroll the opposition.
It all depends on the goals of the people who have gathered to play. The tables and advice in the Creating Encounters section of the DMG give helpful pointers and a basic framework for accomplishing the goals of your group vis-á-vis encounters, but it is only through the artistry of Dungeon Mastering that those goals will be realized.
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